1. Field of the Invention
This invention relates to the field of vehicle monitoring systems. In particular it deals with the method of compressing data for on board storage and subsequent transfer of these data to a computer for analysis.
2. Description of the Prior Art
Prior art vehicle monitoring systems have either provided display means only, with no provision for storage means, or they have used on-board paper or magnetic tape as the storage media, as disclosed in U.S. Pat. Nos. 3,099,817; 3,964,302; 4,050,295; 3,864,731; 3,938,092; 3,702,989 and 3,792,445. Such electromechanical storage means suffer the disadvantages of being unreliable and bulky. Purely electronic solid-state memory has been used, but one of the difficulties of using solid-state memory to provide storage for continuous real-time data, such as has been disclosed in U.S. Pat. No. 4,188,618, is that this approach requires large amounts of memory to achieve the required resolution over a recording period of several weeks. Some systems that have used solid-state memeory have not recorded continuous real-time data. Instead, they compared the raw data to pre-set limits, and recorded only those data which fell outside the limits. A system representative of this approach is the subject of U.S. Pat. No. 4,258,421.
The limitations to this approach are that the raw data are not available for subsequent analysis. One is thus unable to scrutinize the data for events that were within the previously defined limits, since these were not recorded.
Another problem has been the question of how to transfer the on-board data to the off-line computer. There have been several approaches to this problem. Either an intermediate unit was used to transfer the data to the computer, as disclosed in U.S. Pat. No. 4,258,421, or the memory portion of the on-board unit was made removable, in which case some additional unit was still required to read the data and interface to the computer. This latter example has been disclosed in U.S. Pat. No. 4,188,618, which also describes other methods of transferring the data to the computer, each of which requires a separate embodiment.
It is a desirable feature of vehicle recording systems to allow the driver or operator to enter data which are subsequently available as part of the computer report. It is also desirable that these data be presented in a man-readable form (such as English language). The solution to this problem has generally been to provide a separate input device, as disclosed in U.S. Pat. No. 4,258,421. This device may be an alphanumeric keyboard or some other device which presents codes to the recording system.
In the latter case the codes can then be included in the report directly, or they can be translated into man-readable form by the computer. The problem with this approach is that, due to the large amount of information that generally needs to be entered, the driver would need a very lengthy list of all the codes and their meanings.